Unraveling the 3D localization and deformation of responsive microgels at oil/water interfaces: a step forward in understanding soft emulsion stabilizers.

Responsive microgels are deformable submicrometer cross-linked polymeric hydrogel particles that are used as a novel class of emulsion stabilizers. Their flexibility and the triggering of conformational changes by external stimuli lead to several advantages compared to rigid particles used in conventional Pickering emulsions. Despite their rapidly increasing use, several key aspects relating to microgel microstructure and localization at liquid interfaces are still unexplored. We present here a novel characterization that employs freeze-fracture shadow-casting cryo-SEM to disclose quantitative 3D information on the deformation and protrusion of microgels at water/oil interfaces. Despite the bulk pH response (swelling), we report here the unexpected absence of size and vertical position changes as a function of pH at liquid interfaces and interpret the results using simple arguments that link the particle interfacial activity, solvation, and internal deformation. These results pave the way to a deeper understanding of a novel class of soft materials.